Plastic composition



Patented Oct. 8, 1940 PATENT OFFICE anus: msnc'com'osmon David A.Fletcher, Arlington, N. 1., asslgnoi to E. I. du Pont de Ncmours aCompany, Wilmlngton, Del acorporationofDelaware No Drawing.

Application March 7, 1989,

Serial No. 260,339

8 Claims. (Cl. 260-36) Illiis invention relates to plastic compositionsand, more particularly, to molding compositions having a base ofpolyvinyl formal resin.

Polyvinyl formal resins belong to that class of synthetic resins knownas polyvinyl acetals and which are prepared by effecting a complete orpartial hydrolysis of a polyvinyl ester, usually polyvinyl acetate, anda complete or partial condensation of the resulting hydroxyl groups withan aldehyde. In the instance of polyvinyl formal resins, the hydroxylgroups are condensed with formaldehyde. The preparation of polyvinylformal resins and the various modified properties that may be obtainedthrough only partial hy- 16 drolysis of the polyvinyl ester and/orpartial condensation of the resulting hydroxyl groups with formaldehydeare known in the art.

Because of the relatively low thermoplasticity of polyvinyl formalresins, and in order to enhance the toughness and impact-resistance ofthe resulting molded articles, these resins have been used in admixturewith plasticizers but the development of satisfactory compositions hasheretofore been limited by the difllculty of achieving in combinatiomina single composition, a relatively low molding temperature, a relativelyhigh softening temperature, and a high degree of toughness andimpact-resistance. This difliculty has been, of course, in line withthat experienced go with other plastics, i. e.,' that toughness and easeof molding, on the one hand, and softening tem-' perature, on the otherhand, are contradictory requirements, in that the addition ofplasticizer to achieve toughness and low molding temperaa ture has theresult of undesirably lowering the softening temperature of the ultimatemolded article.

It is an obiectof thepresent invention to provide compositions having abase of polyvinyl formal resin and which are outstanding in that theyare readily moldable and of unusually high The above objects areaccomplished according to the present invention by using, as aplasticizer for polyvinyl formal resin in plastic compositions, I analkyl phthalate of the formula C6H4(COOR)I wherein R is a saturatedalkyl radical of 6-8 carbon atoms, inclusive. More specifically, theinvention comprises a molding composition of 100 parts of a polyvinylformal resin, up to 25 parts and, preferably, from 8-19 parts, of analkyl I phthalate or a mixture of alkyl phthalates falling within theabove type formula, and, preferably, l-6 parts of a mold lubricant.

Throughout the specification and claims all parts are given by weight.10

Any single one of the alkyl phthalates of the formula CsH4(COOR)2wherein R is a saturated alkyl radical of 6-8 carbon atoms, inclusive,may be used in the present invention or a mixture of two or more ofthese phthalates litany propor- 16 tion may be used but these phthalatesare available commercially as a mixture including the esters of thevarious saturated aliphatic alcohols having between 6-8 carbon atoms,inclusive, and in actual practice no appreciable advantage has beenfound in using any single ester or incomplete mixture of esters overusing the complete mixture suchas sold commercially.

The following examples, in which the alkyl phthalates' herein consideredare simply desiga5 nated by the formula CaH4(CO0R)2 for convenience,illustrate specific compositions coming within the scope of theinvention: 7

Example I Polyvinyl formal resin. 'CsHdCOOR): 9 Aluminum palmitate 1Example II V 85 Parts Polyvinyl formal resin 100 CsH4 COORlz 13 Stearicacid 2 Example III Parts Polyvinyl formal resin. 100 CsH4 (CODE) 2 18Magnesium stearate 4 5 Example IV I Parts Polyvinyl formal resin.-. 100CoI-IACOOR): 32 so Example 'V 1 Parts Polyvinyl formal resinl00CIH4(CQOR)2 25 Zinc stearat L1 5 55 Example VI Parts Polyvinyl formalresin. 100 CoH4(COOR)2 Opalwax 1 Example VII Parts Polyvinyl formalresin. 100 CcHKCOORh" 1 8 Diethyl phthalate 4 Magnesium stearate 4Example VIII 7 s 'Par'ts Polyvinyl formal resin "a. 100 CoH4(COOR)2 12.Tributylphosp '3 Aluminum palmitate 6 Example IX Parts Polyvinyl formalresin. 100 CeH4(COOR)2 10 Dimethyl phthalate'n; 9 Magnesium stearate 5It will be understood that theabove examples are merely illustrative,the invention in its broadest phase comprising plasticizing a polyvinylformal resin with one or a mixture of alkyl phthalates of the formulaCaH4(C0OB)2 wherein R. is a saturated alkyl chain of from 6-8 carbonatoms, inclusive.

The present invention is broadly applicable to those polyvinyl formalresins in-which the content of polyvinyl alcohol is less than about 20%by weight. Above this approximate limit on the polyvinyl alcohol contentthe moisture-sensitivity of the resin increases and its compatibilitywith the plasticizer decreases sufiiciently to make the .resin lessdesirable for purposes of molding.

Examples 7, 8, and 9 illustrate the use of a composite plasticizer,predominantly CsH4 (COOR) 2,

resin, and particularly upon its viscosity, and also upon therequirements to be met, as regards both plasticizer will be desirable incompositions intended for injection molding than in those intended forcompression molding.

As the examples illustrate, various conventional mold lubricants may beadvantageously used although, to some extent, the herein consideredpalmitate, Opalwax, and the like. They will be used in conventionalproportions, usually of the order of fromabout 1 to about 6 parts per100 parts of the resin.

The compositions herein contemplated are primarily adapted as moldingcompositions but are also of value in the formation of sheets, rods, andtubes. I

One of the outstanding advantages of polyvinyl formal resins plasticizedwith the herein considered plasticizer is. foundin the combination ofgreat toughnessgand high softening temperature of resins so.'plafsticized as compared with the much lower values exhibited by thesame resins plasticized with similar proportions of other plasticizers.

is strikingly illustrated in thefollowing table in which the samepolyvinyl formal resin has been used in all of the compositions. Thistable also shows the excellent form stability of polyvinyl formalcompositions employing the herein considered plasticizer. 1 4

Percentage un- Parts Parts Impact Soft. molding at- '1 Plastlcizsrper'lOO oi Lubricant per-100 oi strength, tenp r (it. lbs.) 60 C. 70 0.

CH (000101.--. 18.3 Magnesium stearate 3.7 6.98 71 0 Trlbutylphosphate18.3 do 3.7 5.68 Low 0.5 Ethox ethylphthalate 21.8 Zinc stearate 6.43.68 Low 8.0' Dime ylsebacate-- 18.3 3. 7 3.66 49 3.1Dimethylphthalatel8. 3 3. 7 2. 66 46 3. 4 Diethylphthslate--- l8. 3 3. 72. 22 46 4. 0 12.2 3.7 2.08- 66 1.5 Dimethylphthalate 6.1 3.7 2H8 56 1.6Dibutylphthalate-.. 18.8 6. 3 ,-1.90 Low I Dibutyltartare 18.3 3.7 1.6445 4.8 Dicyclohexylphthalate 18.3 3.7 1.26- i 63 0 Exact value notdetermined.

dyestuffs, pigments, effect materials, fillers, and g the like, may beincluded in the composition.

The proportion of the plasticizer CsH4(COOR) 2 to be used with apolyvinyl formal resin will depend both upon the character of thespecific It will be observed that the composition typifymg theinvention, appearing as the first item" in thistabulation, presents acombination ofhigh impact strength, high softening temperatureandexcellent form-stability not approached by any of the othercompositions, which typify those of the prior art. I

The following tests were used in establishing I the data in the abovetable:

' Impact Test (Charpu)'1'his has been .con-

ducted as prescribed by the American Society for Testing Materials, withtest specimens approximately 0.250 inch thick. The values given arethose calculated for a thickness 1.000 inch, after measurement of theactual thicknesses of the respective specimens, on the assumption thatthe energy required to break is proportional to the thickness.

Determination of Softening Temperature-The test specimen is a moldedstrip of dimensions 2.50 x 0.50 x 0.50 inches. It is conditioned,- priorto being tested, by storage for atleast 24 hours at room temperature andat 45% relative humidity. -With the 2.50 dimension horizontal and the0.50 inch dimension vertical, the specimen is clamped at one end in adevice adapted to be lowered beneath the surface of a bath of "Nujol orsimilar refined mineral oil. A weight of 27.5 grains is now applied nearthe free end of the piece, the arm of this weight, which tends todeflect the specimen as a beam, being 2.0 inches. The specimen isimmersed in the oil bath, which is heated at a rate of from 2 to 3degrees per minute. An electrical contact gives an alarm when the weighthas dropped by 0.06 inch from its initial position. The temperature ofthe oil at this moment is reported as the softening temperature of thespecimen.

Test of UnmoldinyAn injection-molded circular test piece formed in amold cavity of diameter 1.5 inches and thickness 0.11 inch, gated at theedge, is stored at a temperature of 50 C., in air, for 24 hours. Theresulting decrease in diameter, as measured from the gate to theopposite edge, as a percentage of the initial diameter, is reported aspercentage of unmolding. Absence of shrinkage indicates completeformstability at this temperature; high values are correspondinglyundesirable as indications of the lack of form-stability. A similar testis conducted at 70 C.

The plasticizer CBH4(COOR)2 is also advantageous in that it tends toreduce moisture absorption of polyvinyl formal resins plasticized withit as compared to the moisture absorption of the same resins plasticizedwith conventional plasticizers.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it

50 is to be understood that the invention is not limited to the specificembodiments thereof ex-- cept as defined in the appended claims.

I claim:

1. A plastic composition comprising a polyvinyl formal resin and, as aplasticizer therefor, an alkyl phthalate of the formula CsH4(COOR)2,wherein R. is a saturated alkyl chain of 6-8 carbon atoms, inclusive.

2. A plastic composition comprising a polyvinyl formal resin and, as aplasticizer therefor, a mixture of alkyl phthalates of the formulaCaH4(COOR)2, wherein R is a saturated alkyl chain of 6-8 carbon atoms,inclusive.

, 3. A plastic composition comprising 100 parts of a polyvinyl formalresin and, as a plasticizer therefor, up to 25 parts of a mixture ofalkyl phthalates of the formula CaHdCOOR.) 2, wherein R is a saturatedalkyl chain of 6-8 carbon atoms, inclusive.

4. A plastic composition comprising 100 parts of a polyvinyl formalresin and, as a. plasticizer therefor, from 8 to 19 parts of an alkylphthalate ,of the formula CaH4(COOR)2, wherein R is a saturated alkylchain of 6-8 carbon atoms, inelusive.

5. A molding composition comprising a polyvinyl formal resin and, as aplasticizer therefor, an alkyl phthalate of the formula CcH4(COOR) 2,wherein R is a saturated alkyl chain of 6-8 carbon atoms, inclusive,together with a mold lubricant.

6. A molding composition comprising a polyvinyl formal resin and, as aplasticizer therefor, a mixture of alkyl phthalates of the formulaCcH4(COOR)2, wherein R is a saturated alkyl chain of 6-8 carbon atoms,inclusive, together with a mold lubricant.

7. A molding composition comprising 100 parts of a polyvinyl formalresin and, as a plasticizer therefor, up to 25 parts of a mixture ofalkyl phthalates of the formula CeH4(COOR) 2, wherein R is a saturatedallwl chain of 6-8 carbon atoms, inclusive, together with a moldlubricant.

8. A molding composition comprising 100 parts of a polyvinyl formalresin and, as a plasticizer therefor, from 8 to 19 parts of an alkylpathalate of the formula CcH4(COOR)2, wherein R is a saturated alkylchain of 6-8 carbon atoms, inclusive, together with a mold lubricant.

DAVID A. FLETCHm.

CERTIFICATE OF CORRECTION.

Patent No. 2,217,165. October 3, 191m.

DAVID A. FLETCHER.

It is hereby certified thaterror appears in the printed specification ofthe above numbered patent requiring correction as follows: Page 2, firstcolumn, line 62, in the table, for "dibutyltartare" read--dibutyltartre.teand that the said Letters Patent should be read withthis correction therein that the same may conform to the record of thecase in the Patent Office.

Signed. and sealed this 12th day of November, A. D. 1914.0.

Henry Van Ar sdale, zting Commissioner of Patents.

